In our Infidelity series thus far, we've heard from the cheaters, from those who have been cheated on, and from a psychotherapist and expert on the topic. In this final installment, the Sugars focus on the often-overlooked experience of "the other woman" and the moral responsibility that comes with the role.

They discuss with the novelist and biographer Susan Cheever, who was "the other woman" in an affair...twice.

Dear Sugars,

I’m in love with my best friend. And he’s married. And I’m desperately trying to figure out if I should wait for him.

Some context: he's an artist, I'm a writer. We’ve known each other for years, and for most of that time, we were both married. My marriage produced two amazing kids and a comfortable companionship for many years, but little in the way of passion. Then the companionship faded. In the last two years of our marriage, we slept in separate rooms. It was during this time that my best friend and I started having an affair.

The affair started as coffee and lunch dates and Facebook messages every night (sometimes the back and forth would last an hour or two). After we acknowledged our physical attraction and the affair began in earnest, things escalated quickly. We went from best friends who talked all day long to sex maniacs, finding any way and any place to have sex. We’ve explored every kink we’d ever entertained (and some we’d never even considered) and are amazed and awestruck at how sexually compatible we are. We’re closing in on two years of being together, and the desire has only grown stronger. Not only that, but we still talk all day long, we relate on a creative and artistic level, and we never tire of each other’s company. In fact, we‘re desperate for more. We're in love, madly in love. There's no doubt about that.

At first, we both had immense guilt about what we were doing. Over time, we both came to think that we simply chose the wrong spouses. We wish we'd met each other twenty years ago. We know that our affair is wrong, but at the same time, we truly believe that this is meant to be.

The trouble is, I’m now single and he’s not.

I went to therapy and figured out that the best solution for my marriage was to end it. Luckily, my husband independently reached that same conclusion, and we’ve separated very amicably. There have been a few bumps but mostly, it’s the best-case scenario. We co-parent as friends, and our kids are reflecting that back to us in their happy dispositions.

My best friend is still married, and much to my dismay and despair, he still has sex with his wife. He claims it’s “maintenance sex,” which he’s keeping up for the time being so as not to raise any red flags. He left his job to start a new business and it hasn’t quite taken off yet, and he says he doesn’t want to leave his wife in a lurch. He feels like he needs to stay in this marriage for a little while longer to be able to be financially solvent, for his wife’s benefit and for their kids, and also, so he’s not relying on me for financial support.

He says this “maintenance sex” is the bare minimum — that he doesn’t enjoy it, that she barely tries, it takes five minutes. He says he avoids it as much as he can, that it freaks him out, that it's not the same as what we have by a long shot. He says I should take solace in that. Try as I might, I can’t.

He says he wants to be with me, to marry me. That he’s trying to move things in the direction of leaving his marriage. We’ve talked very pragmatically about our kids all being siblings — we’re both on board. He’s seeing a therapist for the first time, trying to figure out how to make this transition. He says he’s never felt like this about anyone, and I believe that. For my part, I’ve never felt more turned on, cared for, or more loved…

…except when I don’t. Except when I know that they’re having sex or think they're having sex, or even when I know they’re having a nothing-special family day together. It kills me. And then I feel terrible, like I don’t matter to him, and I question everything. It absolutely guts me. This feeling affects me at least once a week, and it’s always exactly the same.

He acknowledges my pain and says he’d feel the same way if things were reversed. He says that we’re worth the wait. But if I’m suffering, even 10 or 20% or the time, is it? If I knew he was going to leave her, if I had some assurance, if I had an idea of when it might happen, maybe I could feel better about those moments. But while he's said that he wants to spend the rest of his life with me, nothing has been guaranteed.

I’m trying to be grateful for the present: for the things we have, which feel so rare and valuable. But these weekly bouts of jealousy and doubt have me feeling stymied. How do I plan a future if I don’t know if the person I love more than anything is going to be in it?Do I leave? Do I stay? And if I stay, how do I stay sane until we can be together out in the open? And if I leave, how do I get over the love of my life?

Outside of my therapist, I have literally no one else to talk to about this, and I’m desperate for an outside perspective. Please help, Sugars.

Sincerely,

Helplessly Hoping

Cheryl Strayed: Helplessly Hoping, what a tortured situation. This jealousy of your lover having sex with somebody else is really natural and normal, and it’s also really natural and normal that your lover would be having sex with his wife. That’s the deal, when you are the other woman involved with a married man. We don’t know if he’s going to stay or leave. We know some men leave their wives and marry the other woman, and some men drag it on for years and never leave.

Steve Almond: The central question here is, “Do I really trust that this guy is going to leave his wife?” Right at the center of your wrenching letter is the sentence, “If I knew he was going to leave her, if I had some assurance…” You don’t. And when people are under the spell of love, they say all kinds of things, like, “I promise I’m going to leave.” I’m not saying the man that you are in love with is lying to you, but inner turmoil is telling you that you need him to give you an honest accounting. The question you need to ask him is, “What is the meaning of this affair to you?”

Cheryl: One of the weirdest parts, I’m going to guess, about being the Other Woman, is that you are intimate with one member of a marriage, but not with both. You are both intimate and utterly excluded. That’s part of the agony of this. My questions are, how serious is your lover about making this transition? How does he respond to your request that you actually make some plans together? You might have a lot to worry about. That anxiety you feel, that maybe he never will leave, might speak to the truth of the situation.

Steve: There are cases where part of the turn-on is that it is an affair. It is possible that it’s something about marriage itself that deadens this man and his passion. You don’t want to wind up, four or five years down the road, being the person with whom he is having maintenance sex, and realizing that you, or he, or both of you, need to go outside the marriage to find the kind of charge and connection that you have found with each other. I’m not saying that’s necessarily going to happen, but often the person outside the marriage doesn't realize that part of the charge is that they are forbidden. When they are suddenly the morally-approved safe mate, a lot of the charge, connection, and intimacy dies off.

Cheryl: Helplessly Hoping, you might think, “He’s married to somebody else. He says he loves me, but he doesn’t have any commitment or obligation to me.” But he does. So I would strongly encourage you to put an end date on your suffering. You get to be in charge of how long you’re willing to agonize in this state of unknowing. There are all kinds of solutions that you two can come up with together, but you can only do it if you address it head-on. Make a plan. You really do deserve to move forward in your life, with this relationship or without it.

Dear Sugars,

I’m a single mom in my early 40's. My teenage kids are the loves of my life. We have an amazing, close relationship and I couldn't be more proud. I am the sole provider for our family, so my life is quite busy.

Five years ago, a friend — let's call him B — turned into an occasional lover. I was not naïve about what we had. I’m seven years older than he is and from a very different cultural background. As much as we tried to not get too intertwined, it inevitably happened, and very quickly, our relationship became emotionally charged. We spent a lot of time together. We also work together. We had sleepovers, dinners, movies, endless lovemaking, but no prospect of a future together.

About a year into our relationship, B broke it off with me to find a more age appropriate, culturally acceptable, practical wife without baggage. As much as I knew this beautiful, intense affair would end, I had no idea how hard it would hit me. I won't go into the sappy details, but our break-up shook me to the core and it took a year for me to be able to breathe when I saw him in the hallways at work.

Over the past three years, after much healing and a string of failed relationships, I’ve tried to date and I’ve invested a lot of time in finding the right mate. I went on as many dates as my super busy life allowed. I wrote and answered hundreds of emails on online dating sites. I was always honest and straightforward with the men I met about seeking a meaningful relationship, not a short lived hook-up. Most of them (not all) completely lied, and after I had sex with them, they dumped me after a few weeks. So I swore off dating and went back to my drama-free single life.

Last year my former lover, B, got married. I felt genuinely happy for him and had no bad feelings about it. I did sadistically engage in peeking at his wedding pictures online. He looked happy, but I felt OK! Two months after he wed, he approached me at work and told me how much he misses me and the sex we had. This was the first time we spoke in over two years! Before I could say anything, he grabbed me and started kissing me with a passion I so well knew but left in my past. When I could finally speak, I told him he was completely insane and to leave me alone. He cornered me like this a few more times in the next couple of months, and every time he touched and kissed me, I was on fire. I was completely hooked again. I managed to fight him off and again told him to leave me alone and go home to his wife. That's what bothered me the most — he's cheating on his wife! With me! Awful! What if I was the wife? How would I feel? I wanted no part of this.

Six months later, he showed up at my door. The sex was incredible, like unleashing a caged animal that's used to living free. We couldn't get enough of each other. It was indescribable. We never spoke. Not a word. Then he left. To my shock, I didn't feel any guilt, any pain. I felt mounds of joy! I felt happy, satisfied, fulfilled, complete.

Soon after, this became a regular affair. Every time I tried telling him enough, he would show up and I wouldn't say no, so I stopped fighting it. I try to rationalize things and say to myself that I'm single, so it's not my problem, but his. But is it?

With love,

The Paramour’s Dilemma

Susan Cheever: In this life, we can do whatever we want. The question is, do we have a moral and ethical system that we want to adhere to? That’s a big question, and she doesn’t answer it. If she wants to do unto others as she would have them do unto you, she probably shouldn’t be doing what she is doing.

Steve: The Paramour’s Dilemma says the first time he came to her, he starts kissing her passionately, and she’s on fire, but the moment she can speak again, she’s really morally troubled. Then there’s this curious moment in the letter where he shows up at her door and suddenly they are having sex again, as if she has just leapt right past her conscience and the understandable reluctance she would have to enter into a relationship that involves betrayal. He is the central player, but she is also conscious of the fact that she is party to this as well.

Cheryl: What she’s saying is, “I love the sex, and this is a great setup for me right now. Yet, is this wrong? Should I allow myself to enjoy this? Because I know I am in some ways breaking my ethical code.” She’s of two minds.

Steve: She writes, “As much as I knew this beautiful, intense affair would end, I had no idea how hard it would hit me.” I want to note that the reason this guy broke it off with her was to find somebody who was a more “age appropriate, culturally acceptable, practical wife without baggage.” Swimming under the surface of this is, she’s not good enough to present in public. She’s good for hot, electrifying sex. There’s something in that that feels degrading.

Susan: But she is saying, she knows that this is going nowhere, but it’s too good to give up. My inclination is to believe her. The problem that we’re given is not, “Is he going to hurt her again?” It is, “Is it OK for her to sleep with someone? Can she tell herself that the cheating is really her problem?”

Cheryl: When I turned away from an affair I almost had, part of it was to protect my own life, and part of it was because I felt like I was going to be doing something wrong to another woman. I don’t want to bring pain and sorrow into somebody else’s life if I can help it. Obviously, that’s not the only thing that guides me. It’s the code that I aspire to. And many of us fall short of that all the time. I’m going to guess that this man’s wife has no idea that her husband is cheating on her, and it’s going to be devastating.

New episodes of Dear Sugar Radio are released weekly. Do you have a question for the Sugars? Email dearsugarradio@gmail.com.

Amory SivertsonTwitterProducer for New ProgrammingAmory Sivertson is an associate producer for new programming at WBUR. She's one of the producers of Modern Love: The Podcast.